The invention relates to a floating-caliper disc brake of the type with a brake carrier arranged fixedly on one side of a rotating brake disc. Two brake pads are provided which are each located adjacent to respectively one side of the brake disc and which are displaceable in the direction of the brake-disc axis and are supported on the brake carrier, in the peripheral direction of the disc, in order to transmit the braking torque. A floating caliper engages over the brake disc, is guided displaceably on the brake carrier in the direction of the disc axis, carries a brake piston supported on one brake pad, is supported on the other brake pad and, in its caliper part supported on the first brake pad, is more pliant on the run-out side than on the run-in side.
In those floating-caliper disc brakes having a floating caliper designed as a claw caliper engaging over the brake disc, uneven wear of the brake linings of the two brake pads occurs after even a relatively short time. This is especially so when they are used in heavy vehicles under high stress, specifically in that the brake lining of the brake pad which can be pressed against the brake disc by the brake piston undergoes greater tangential wear on the disc run-in side, relative to the forward direction of rotation of the brake disc, and the brake lining of the brake pad which can be pressed against the brake disc by the floating caliper experiences greater tangential wear on the disc run-out side.
The brake linings therefore wear in opposite directions to one another obliquely in relation to the plane in which is located the brake-disc endface adjacent to them.
This tangential oblique wear of the two brake linings is mainly caused by an elastic deformation of the brake carrier resulting from peripheral forces (braking forces). This results in the claw caliper mounted on the brake carrier being likewise shifted obliquely relative to the brake disc, and consequently the tangential wear of the lining is increased even further.
At the same time as this tangential oblique wear, radial oblique wear of the linings also occurs on disc brakes equipped with a claw caliper. This occurs because the clamping device formed by the claw caliper and the brake piston yields elastically under the effect of the clamping force. Consequently, the brake linings are not pressed against the brake-disc faces with a uniform pressure in the radial direction.
Both types of oblique wear (tangential as a result of deformation of the brake carrier under peripheral force and radial as a result of deformation of the claw caliper under clamping force) are, in the final analysis, due to uneven pressure exerted on the linings and cause an increase in the length of travel when the brake is operated.
To reduce or prevent tangential oblique wear, there are already known floating-caliper disc brakes, in which a special guide for the floating caliper on the brake carrier is provided for this purpose, that is to say this problem has been solved in a purely mechanical way see German Offenlegungsschrift No. 2,907,517; Great Britain patent specification No. 1,112,988; German Patent Application No. P 34 11 600).
There are also known floating-caliper disc brakes, in which the floating caliper has in places greater pliability in the peripheral direction of the disc (German Offenlegungsschrift No. 2,831,643 and German Patent Specification No. 3,121,186).
In these constructions, the floating caliper is supported on one brake pad by means of two claws arranged at a distance from one another in the Peripheral direction of the disc.
Where the brake construction according to German Offenlegungsschrift No. 2,831,643 is concerned, here the floating-caliper claw located on the run-out side relative to the forward direction of rotation of the brake disc has greater pliability.
Consequently, when the brake carrier pivots inwards as a result of deformation under the influence of braking forces, the floating caliper can give way elastically on the run-out side and thereby prevent tangential oblique wear. However, radial oblique wear is not prevented and is even increased because of the flexible floating-caliper claw.
In contrast, in the brake constructon according to German Patent Specification No. 3,121,186, the floating-caliper claw located on the run-in side has greater Pliability. However, this merely ensures that the vibrations caused by friction at the front edge of the outer brake lining are prevented or at least greatly reduced. This construction does not counteract oblique wear of the brake pads.
Finally, a floating-caliper disc brake of the type referred to above is already known (German Offenlegungsschrift No. 3,347,387). In this arrangement, in order to reduce tangential oblique wear of the brake pads, the floating-caliper has the greater pliability on the run-in side in the region of the caliper web engaging over the brake disc.
An object on which the invention is based is, in a floating-caliper disc brake of the above-noted type, to prevent both tangential and radial oblique wear of the brake linings, especially under high brake stress.
According to the invention, this object is achieved by both asymmetrically mounting the piston vis-a-vis the brake pad being actuated and by constructing the frame legs of the caliper to be more pliant on the run-out side than the run-in side. Also the longitudinal frame leg supporting the brake pad at the side of the disc opposite the piston extends to the level of the piston.
The advantage of constructing the floating-caliper as a frame according to the invention and of designing it specially for strength in the region of connection of its two transverse frame legs on the longitudinal frame leg supported on one brake pad is that, at the connecting point located o the run-out side, the floating frame has special elastic flexibility under the influence of the pressing forces bringing the brake pads into engagement with the brake disc. It is thereby possible for the pressing force exerted by the longitudinal frame leg on the brake pad supported on the latter to be applied asymmetrically, in such a way that it is lower on the run-out side than on the run-in side. This appropriately compensates the tangential wear of this brake pad which results from the deformation of the brake carrier and which occurs on the run-out side, so that a plane-parallel wear behaviour is obtained.
In contrast, the tangential oblique wear of the brake pad interacting directly with the brake piston or located on the same side as the piston is eliminated because the offset of the point of engagement of the brake piston on the brake pad in the direction of the run-out side of the brake carrier causes force to be exerted asymmetrically, as a result of which the tangential wear of this brake pad occurring on the run-in side can likewise be compensated.
In addition, arranging the longitudinal frame leg, supported on one brake pad, level with the brake piston results in a large-area support of the brake lining on the same side as the frame, this support remaining substantially plane-parallel relative to the brake-disc face under the stress of the clamping force and thus counteracting the formation of radial oblique wear of the brake pad.
Advantageous preferred embodiments of the invention optimally arrange the brake carrier to facilitate its ideal design in terms of rigidity. The reduction in the elastic deformation of the brake carrier, which can be obtained by designing it according to certain preferred embodiments, makes it possible to reduce correspondingly the asymmetry provided according to the inventin in the support of the brake pads (deliberate frame pliability on the one hand and the offset of the brake piston on the other hand) and to coordinate the components of the brake with one another in terms of their deformation behaviour.
At the same time, by taking the proposed measures into account, it becomes possible according to the invention to design the brake carrier and floating frame so that these parts can be coordinated with one another in such a way that an ideal wear behaviour of the brake pads is achieved, whilst at the same time ensuring the least possible weight of the parts.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.